1. Field of the Invention
The current invention relates to a reactor for biological, in particular anaerobic, purification of waste water including a reactor vessel having a substantially flat or round bottom, at least one supply line arranged in the lower region of the reactor vessel for feeding waste water to be purified into the reactor, at least one fluid discharge pipe for discharging purified waste water from the reactor, and at least one discharge pipe for solid matter arranged in the lower region of the reactor vessel for discharging solid matter from the reactor.
2. Description of the Related Art
A multitude of mechanical, chemical and biological methods and corresponding reactors are known for waste water purification. In biological waste water purification, the waste water to be purified is brought into contact with aerobic or anaerobic micro-organisms, which in the case of aerobic micro-organisms decompose organic contaminants contained in the waste water predominantly to carbon dioxide, biomass and water, and in the case of anaerobic micro-organisms mainly to carbon dioxide and methane and only in small part to biomass. In recent times the biological waste water purification methods are carried out increasingly with anaerobic micro-organisms whereby the reactors, depending on the type and form of the utilized biomass, are categorized for anaerobic waste water purification into contact sludge reactors, upflow anaerobic sludge blanket (UASA) reactors, expanded granular sludge bed (EGSB) reactors, fixed bed reactors and fluidized bed reactors. Whereas the micro-organisms in fixed bed reactors adhere to stationary carrier materials and the micro-organisms in fluidized bed reactors adhere to freely moving, small carrier material; the micro-organisms in UASB and EGSB reactors are utilized in the form of so-called pellets.
In the case of UASB and EGSB reactors, waste water which is to be purified, or a mixture of waste water which is to be purified and already purified waste water from the outlet of the anaerobic reactor, is fed continuously to the reactor through an inlet which is arranged in the lower region of the reactor and is directed through a micro-organism pellet-containing sludge bed which is located above the inlet. During decomposition of the organic compounds from the waste water, the micro-organisms form methane and carbon dioxide containing gas (which is also referred to as biogas) which partially adheres to the micro-organism pellets in the form of small bubbles and which partially rises to the top in the reactor in the form of free gas bubbles. Because of the added gas bubbles the specific weight of the pellets decreases, which is the reason that the pellets rise to the top in the reactor. In order to separate the formed biogas and the rising pellets from the water, separators are arranged in the center and/or upper part of the reactor, mostly in the embodiment of gas hoods under the top of which biogas accumulates, forming gas cushions. Purified water, relieved of gas and micro-organism pellets rises to the top in the reactor and is drawn off at the upper end of the reactor through overflows.
Moreover, during operation of the reactor, solids continuously float downward in the reactor and settle on the reactor bottom from where they are discharged from the reactor through a solid matter discharge pipe. These are, on the one hand, solids contained in the waste water and, on the other hand, solid matter which initially only forms in the reactor, for example in the situation where waste water having a high content of dissolved calcium is used—as for example waste water from the paper industry. Due to chemical conditions, a portion of the calcium precipitates as solid calcium-carbonate. Since the solid matter settles uniformly across the reactor cross section, not all solid matter sediments can be removed in practice from the reactor through the solid matter discharge line. Therefore, large areas of sediment accumulate increasingly on the reactor bottom and in particular at right angle locations in the reactor vessel. In order to remove these sediments from the reactor, the reactor must be shut down from time to time.
To overcome this problem, reactors for biological purification of waste water have been suggested, for example in DE 40 42 223 A1, whereby the lower reactor section tapers conically in the downward direction. This ensures that at least the greater portion of the sediment accumulates in the tip of the cone from where it can be easily discharged from the reactor through a solid matter discharge pipe. This lower conical reactor section must, however, be manufactured from a particularly stable material in order to be able to withstand the weight of the waste water contained in the possibly several meters high reactor. Moreover, manufacture of a reactor of this type is very complicated and therefore expensive.
What is needed in the art is a reactor for biological, in particular anaerobic, purification of waste water from which solid matter occurring during its operation can be easily and in particular completely removed and which is of simple design and can be produced cost effectively. The reactor is to be suitable for purification of calciferous waste water, for example from the paper industry.